Effect of Sedimentary Facies Characteristics on Deep Shale Gas Desserts: A Case from the Longmaxi Formation, South Sichuan Basin, China
Round 1
Reviewer 1 Report
Shale gas exploration and development is currently a hot spot of unconventional oil and gas resources. Especially in North America and China, there are many achievements in shale gas exploration and research. With the breakthrough of exploration technology, the exploration and development of deep shale gas in China has become a major trend. At present, there are few achievements in deep shale research. The author has carried out a large number of basic experiments for the study area to analyze the impact of sedimentary facies types on high-quality reservoirs, this is of reference significance for exploration in other regions. At present, several issues need to be revised:
1.The article deals with shale reservoir heterogeneity in many places, but the introduction only briefly introduces the research results, and it is suggested to increasing the main understanding of shale heterogeneity in recent years.
2. For the interior of the key exploration interval, four sub-layers are divided. It is suggested to draw pictures for vertical comparison of the mineral composition, physical properties and other characteristics of each sub-layer, which is more intuitive
3. Please supplement the correlation diagram between organic matter content and physical properties, clay mineral content, etc. The author has marked it in the article, but I can't find the picture.
4. In the figures showing the microscopic characteristics of shale (SEM, CT), it is necessary to mark the mineral type and pore type to make it easy for readers to read.
5. How does the presence of organic matter affect shale reservoirs? Need to be summarized
6. What effect does the type of sedimentary facies have on the type of reservoir minerals?
Author Response
1.The article deals with shale reservoir heterogeneity in many places, but the introduction only briefly introduces the research results, and it is suggested to increasing the main understanding of shale heterogeneity in recent years.
Response:According to the opinions of the reviewers, we have added the latest research on shale heterogeneity. (Line 53-62;Line 77-88)
2.For the interior of the key exploration interval, four sub-layers are divided. It is suggested to draw pictures for vertical comparison of the mineral composition, physical properties and other characteristics of each sub-layer, which is more intuitive
Response: We have made modifications based on the reviewer's suggestions(Iine 575-577)
3.Please supplement the correlation diagram between organic matter content and physical properties, clay mineral content, etc. The author has marked it in the article, but I can't find the picture.
Response: Considering the Reviewer's suggestion, We have supplemented figures in the article (Line697-699)
4.In the figures showing the microscopic characteristics of shale (SEM, CT), it is necessary to
Response: Considering the Reviewer's suggestion, We have marked the mineral type and pore type
5.How does the presence of organic matter affect shale reservoirs? Need to be summarized
Response: Considering the Reviewer's suggestion, We have summarized the impact of organic matter on the development of shale reservoirs(line 683-687)
6.What effect does the type of sedimentary facies have on the type of reservoir minerals?
Response: After seriously considering the problem of reviewers, We have conducted sufficient research to clarify the impact of sedimentation on mineral characteristics.(line 477-481,Line 558-565)
Reviewer 2 Report
In recent years, there have been many research achievements on shale gas, but the research on deep shale is relatively small. The author's research on the relative sweet point effect of deep shale reservoir sedimentation has certain innovation. The article has carried out detailed research on shale lithofacies, lithofacies, sedimentary structure, organic matter, pore structure and other aspects, and defined the distribution characteristics of high-quality reservoirs, Research methods and understanding are of great significance for shale gas exploration. However, there are still some details to be improved in the article at present:
1. The paper of the article needs language polishing
2. The introduction of the article needs to be improved, especially the research results of shale heterogeneity need to be increased in recent years.
3. The introduction of nano-CT in the Materials and methods part needs to be supplemented
4. In the sedimentary model part, it is necessary to elaborate the overall sedimentary facies characteristics of the study, especially the facies zone of high-quality reservoir development.
5. Generally speaking, the internal pores of shale are divided into organic pores and inorganic pores. Is there any difference in the impact on these two types of pores on the reservoir?
6. The influence of sedimentary facies difference between the enrichment of organic matter and the development of organic matter pores needs to be supplemented.
Author Response
1.The paper of the article needs language polishing
Response: According to the reviewer's comments, we have polished the language of the full text after revising the content.
2.The introduction of the article needs to be improved, especially the research results of shale heterogeneity need to be increased in recent years.
Response:According to the opinions of the reviewers, we have added the latest research on shale heterogeneity. (Line 53-62;Line 77-88)
3.The introduction of nano-CT in the Materials and methods part needs to be supplemented
Response: According to the reviewer's comments, These contents have been supplemented（line 197-201）
4.In the sedimentary model part, it is necessary to elaborate the overall sedimentary facies characteristics of the study, especially the facies zone of high-quality reservoir development.
Response: According to the opinions of the reviewers, These contents have been supplemented (Line 235-252)
5.Generally speaking, the internal pores of shale are divided into organic pores and inorganic pores. Is there any difference in the impact on these two types of pores on the reservoir?
Response: According to the reviewer's comments, the impact of these two types of pores on reservoir development has been described in the article.(line 448-454,line683-687 )
6.The influence of sedimentary facies difference between the enrichment of organic matter and the development of organic matter pores needs to be supplemented.
Response: According to the opinions of the reviewers, These contents have been supplemented (Line 476-480, line 492-497)
Reviewer 3 Report
In this paper, the authors investigated sedimentary characteristics, mineral composition, pore structure, and controlling 2factors of high quality reservoir development on the basis of thin section, scanning electron microscopy（SEM）and QEMSCAN analysis, X-ray diffraction (XRD), total organic carbon (TOC), Nano-CT scanning and Low-pressure N2 adsorption on shale samples from the Longmaxi Formation in South Sichuan Basin. This paper is overall well written and there is a large amount of data and analysis provided from various perspectives. I this paper can be accepted after minor revisions and author's response to the following comments: 1) The methods part is very concise and should be expanded in detail. You need to at least refer to articles or mention what procedure exactly is followed? 2) You have presented the adsorption-desorption curves at the end without the PSDs. Please move that up and add the PSD curves for the curves. 3) You dont need to bold the last paragraph of the introduction.4) In the last paragraph you have talked about U/Th ratio. Where is that data and how was that obtained?
Author Response
1) The methods part is very concise and should be expanded in detail. You need to at least refer to articles or mention what procedure exactly is followed?
Response: We have made correction according to the Reviewer's comments.
2) You have presented the adsorption-desorption curves at the end without the PSDs. Please move that up and add the PSD curves for the curves.
Response: We have made correction according to the Reviewer's comments. (Line 670-672)
3) You dont need to bold the last paragraph of the introduction.
Response: According to the opinions of the reviewers, We have made changes in the article (line 107-113)
4) In the last paragraph you have talked about U/Th ratio. Where is that data and how was that obtained?
Response: In order to compare the characteristics of shale heterogeneity in the longitudinal direction, the U/Th value data is mainly compared using the collected logging data. Due to the large number of logging data values, only the statistical results are compared in the article. In order to clarify the source of the analysis results, we have explained them in the article (line 705-709)
